1. Field of the Invention
The present invention relates to a method and an apparatus for carrying out a plasticization, i.e. an even softening, of a molding material. More particularly, it relates to a method and an apparatus for supplying a molding material to a cylinder having a built-in screw, to plasticize the molding material.
2. Description of the Related Art
When a molding material, for example, a thermoplastic material or a ceramic material combined with a binder, is molded by injection molding, extrusion molding or a blow molding, usually, a method of carrying out the plasticization, whereby the molding material is supplied to a heated cylinder in which a screw is rotated, to thereby plasticize the material, is used.
Recently, in such a plasticization method, to improve such physical properties as the strength of the molded products, a development of a ultra high-molecular weight the plastic material, an addition of large amount of inorganic fillers, and a reduction of the binder content when the material is a ceramic material, have been carried out.
Nevertheless, the plasticizing of molding material, such as a ultra high-molecular weight plastic materal, an inorganic-filled plastic material or a ceramic material having a low binder content in a short time is difficult. In addition, when such plasticization is carried out, a compression zone of the screw may suffer conspicuous wear.
To overcome the above disadvantages, a method of applying ultrasonic waves to a nozzle portion of the screw or a tip of an extruder is disclosed in Japanese Examined Patent Application (Kokoku) No. 45-39954 (JPP 45-39954).
In the method disclosed in the JPP 45-39954, the apparent viscosity of the molding material is reduced by the appllication of ultrasonic-waves, and thus the time required for carrying out the plasticization is shortened and abrasion of the screw is greatly reduced.
Nevertheless, the prior art method suffers from the following disadvantages:
(1) In general, the plasticizing of a material supplied to the cylinder is mainly started at one side of a cylinder wall, and thus it is not always possible to carry out an even plasticization of the material in all parts of the cylinder. The application of ultrasonic waves to the screw eliminates the above problem, but the effect thereof is very limited, and accordingly, the prior art method does not fully overcome the problem.
(2) A mere application of the ultrasonic-waves to the screw has less effect.